1. Field of the Invention
The present invention relates to a rubber-based aqueous pressure-sensitive adhesive composition and a pressure-sensitive adhesive tape employing the aqueous pressure-sensitive adhesive composition. The pressure-sensitive adhesive tape of the present invention can be applied to various kinds of uses to which a pressure-sensitive adhesive tape comprising a rubber-based pressure-sensitive adhesive layer as a pressure-sensitive adhesive layer has conventionally been applied. The pressure-sensitive adhesive tape of the present invention is useful as a pressure-sensitive adhesive tape for electrical insulation. And the pressure-sensitive adhesive tape is available, for example, a pressure-sensitive adhesive tape for protecting or binding a wire harness of automobiles, a pressure-sensitive adhesive tape for insulation used for layer insulation and exterior insulation of electrical parts and electronic parts such as transformers and coils, a pressure-sensitive adhesive tape for display and a pressure-sensitive adhesive tape for identifying. In particular, the pressure-sensitive adhesive tape is useful as a pressure-sensitive adhesive tape for protecting or binding a wire harness of automobiles. In addition to the above, the pressure-sensitive adhesive tape of the present invention can be applied to pressure-sensitive adhesive tapes for various kinds of uses such as a pressure-sensitive adhesive tape for corrugated fibreboard packaging, a pressure-sensitive adhesive tape for medical treatment and a pressure-sensitive adhesive tape for masking. The pressure-sensitive adhesive tape of the present invention is used in a tape or sheet shape.
2. Description of the Related Art
Rubber-based pressure-sensitive adhesives have conventionally been used as pressure-sensitive adhesives. A blend of a tackifier into a base resin has generally been used for these pressure-sensitive adhesives. A solvent type has been in the mainstream as these pressure-sensitive adhesives; however, in view of social request and tightened regulation for environmental protection, resource saving, and safety and health, desolventization is an important problem and a substitute for solvent type pressure-sensitive adhesives has been demanded. Aqueous pressure-sensitive adhesives using rubber-based latex have been used in various kinds of uses as pressure-sensitive adhesives substituting for the above-mentioned solvent type pressure-sensitive adhesives in view of versatility and possibility of the development of applications.
Such rubber-based aqueous pressure-sensitive adhesives are aqueous emulsion, so that stability of the emulsion, particularly, stability for mechanical shear is emphasized for one of performance requirements. Such mechanical stability is stability for mechanical shear applied in gear pumps and roll coaters, and additionally stability for mechanical shear applied during spray coating increased in a coating system in recent years. The case where such mechanical stability becomes poor causes agglomerate in the emulsion to deteriorate commercial value. It has been proposed for mechanical stability of such aqueous pressure-sensitive adhesives that a tackifier resin emulsion obtained by emulsifying a tackifier resin in the presence of an emulsifier and a protective colloid be used as the tackifier for rubber-based latex (Japanese Unexamined Patent Publication No. 7-133473). However, according to the patent, mechanical stability can be improved to some degree and yet is not sufficiently satisfactory.
With regard to rubber-based aqueous pressure-sensitive adhesives, required performance becomes equal to solvent type pressure-sensitive adhesives and is of a higher order with expansion of uses thereof. For example, in the case where rubber-based aqueous pressure-sensitive adhesives are applied to a pressure-sensitive adhesive layer of a pressure-sensitive adhesive tape for electrical insulation, electrical insulation properties are required; however, rubber-based aqueous pressure-sensitive adhesives are insufficient in insulating characteristics by reason of containing a water-soluble ionic emulsifier in very large quantities. Rubber-based aqueous pressure-sensitive adhesives are not sufficient also in moisture-proof adhesive strength under humidification.